Coded track circuit signaling system



May '28; 194% N. D. PRESTON CODED- TRACK CIRCUIT SIGNALING SYSTEM Original Filed Nov.

INVENTOR Patented May 28, 1946 CODED TRACK CIRCUIT SIGNALING SYSTEM Neil 1). Preston, Rochester, N. Y., assignor to General N. Y

Railway Signal Company,

Rochester,

Original application November 9, 1940, Serial No. 365,065. Divided and this application August 22, 1944, Serial No. 550,543

12 Claims.

This invention relates to so-called coded track circuits for railroads, and more particularly to the provision of means for protecting the track relay operated by the inverse or off-code pulses from being improperl coded if a stray or extraneous potential across the track rails should exist at a time when the inverse pulses are cut off and this track relay should not operate.

This application is a division of my co-pending application Ser. No. 365,065, filed November 9, 1940, now Patent No. 2,371,263 dated March 13, 1945, and entitled Coded track circuit signaling system; and no claim is made herein to subject matter disclosed in such parent application.

In the conventional coded track circuit, to which this invention relates, a battery or other source of current at one end of a track section is intermittently applied across the track rails to energize and deenergize a code following track relay at the other end of the section in accordance with a suitable code pattern, which is usually the rate of the intermittent energization. The character or rate of this transmitted or driven code may be changed to conform with trafiic conditions, or the like, and thus provide for the transmission over the track rails of (linen.

ent conditions of control for governing the indication of signals, or the like, as well as detecting the occupancy of the track section.

In certain applications of such coded track cir. cuits, it is desirable to provide another track relay at the feed or driving end of the track section which is energized by what ma be termed inverse or oil-code pulses existing during the deenergized or off periods of the regular driven code,

In the usual arrangement for a coded track and deenergized intermittently as it is connected to and disconnected from this stray potential by operation of the code transmitter, and will not stop its coding operation as it should when the off-code pulses cease. In other Words, the code transmitter for the driven code may act in the presence of a stray current to cause a false selfcoding action of the off-code track relay intended o r spond to only the off-code pulses transmitted from the other end of the track circuit, and thereby create an unsafe condition if the inverse code is relied upon for safety.

This false self-coding of the oii-code track relay by a stray current is particularly objectionable Where the inverse code is out 01? before a train enters the section for the purpose of relaying some desired control over a plurality of track circuits. When a train enters a coded track circuit section at the end receiving the transmitted or driven code it, of course, tends to shunt the off-code track relay at the other end; but it may happen that a linear impedance of the rails, particularl if there is high resistance bonding together with a sufficient inter-rail stray potential maintained in spite of the wheel shunt, will allow sufficient current to flow through the oifcode relay to cause its improper operation.

The primary object of the present invention is to provide a coded track circuit organization affording an inverse or ofi-code which is automatically checked or protected against false coding operation in the presence of a stray current, so that the inverse code may be relied upon safel to govern approach locking relays, indications of opposing signals, or the like.

Generally speaking, and Without attempting to define the exact nature and scope of the invention, it is proposed to protect against such improper coding of the off-code track relay in the presence of stray current by requiring this relay, in order that its operation will be effective to indicate the presence of the inverse code, to release positivel during each ofi period of the transmitted code, such release occurring in the case of the legitimate inverse code pulses, but not in the presence of a stray current capable of falsely energizing Said relay when the inverse code pulses are removed In this embodiment of the invention, the oil'- code track relay must release during the oil period of the transmitted code as determined by the transmitting relay 'or equivalent in order to produce any effect upon the relay means or decoding apparatus governed by said track relay, so that if this track relay is held up by the stray current until after the transmitter has acted to disconnect it from the track rails, there is no decoding action and no false indication of the presence of the legitimate inverse code pulses.

Various other objects, characteristic features and attributes of the invention will appear as the description progresses.

The accompanying drawing illustrates in a simplified and diagrammatic manner one specific embodiment of the inventiomthe nature of the illustration being designed to facilitate an understanding of the principles and mode of-operation of the invention rather than'to show'theexact arrangement and construction of parts that might be employed in practice.

The single figure of drawings illustrates one embodiment of the invention in a simple form applicable to various conditions and systems of trafiic control for railroads, and this particular form has been shown with respect to a single insulated track section assumed to be one of many employed throughout a stretch of railway track.

Refeiringto the drawing, it is assumed that the coded track circuit is of the conventional direct current type, using primary batteries, or trickle-charge storage batteries as a source for the track circuit current, but it should be understood that the same principles may be applied to coded track circuits energized from alternating current sources. It is also contemplated that transmitted or driven codes of different rates, such as '75 and 180 on and off periods per minute will be'obtained from a suitable code generating device,- such as the code oscillator in accordance with the usual practice, the contacts of such an oscillator being illustrated diagrammatically as Cl80 and C75. For the purpose of this" disclosure, contacts ClBil and C are ass ii me d to be on separate oscillators which are normally. operating at their respective rates. The

selection between the different code rates to be suitable manner, and the relay X is typical or illustrative of a means suitable for this purpose. the particular arrangement illustrated, it is assumedthat a transmitted or driven code from right toleft, as indicated bythe solid arrow, will be employed for governing indications of a' wayside signal I, and that an inverse or off codein'the other directicn. as indicated by the dotted arrowf'will be employed to control the energization of a relay OCI-ll controlling the indicatio'ns'of some other signal, the approach looking equipment for a switch or for some other purpose. "It is further contemplated that the inverse or off code may be controlled by the presence of a train in one or more adjoining track sections, or in some other manner, dependent upon the use of the coded track circuit; and the relay Y is typical or illustrative of such a means for cutting off the inverse code prior to and independently of the entrance of a train into the section.

In the arrangement illustrated, the coder or oscillator contacts Cl'ilfl or 015 as selected by relay X energize a-repeater or transmitter relay CP, assumed to be of the two-position biased pola'r'type', which when energized with its operating polarity shifts its contact fingers 4 and 22 tothe left, the contact 4 connecting the track battery 5 across the track rails in series with a limiting resistance 6 in accordance with the usual mitter relay CP acts to control through a transformer 2i the off-code relay OCH which relay OCH in turn acts through a decoding transformer -39 to maintain the repeater relay OCI-IP picked up so long as legitimate off-code pulses are received.

The significant feature characteristic of this invention is that the off-code track relay OCTR is not prevented from being operated intermittently in the presence of a stray current, but is not effective to have any controlling effect upon the off-code responsive means if a stray current exists. In other words, the self-coding of the off-code track relay OCTR is not prevented, but this relay OCTR is not effective to produce any controlling effect on the relay OCHP if such coding operation is due to a stray current instead of legitimate off-code pulses.

The decoding apparatus and means for transmitting off-code pulses at the other end of the track section may be of any suitable arrangement in accordance with regular practice. As illustrated, an impulse relay IMP of the two-position biased polar type and arrange to act, when deenergized and its contact finger H is moved to the left, to connect the code following track relay CFTR across the track rails, and when energized to connect the battery ll for'theoff-code pulse across the track rails. The contact finger E2 of the code following track relay CFTR energizes alternately the two halves of the primary of a decoding transformer l3 having a mid tap in accordance with the usual practice, and one secondary of this transformer is connected through rectifying contacts M on this track relay CF'I'R to a relay ll-I, which is'energized so long as the code following track relay is coded regardless of its code rate. Another secondary-of the decoding transformer is arranged to energize a circuit including condenser 29 and tuned for the higher code rate for impulsing the primary of the transformer I 6, the secondary of which is connected through a full-wave rectifier l! to a relay 1) for indicating that a code of the 180 rate is being transmitted. The relays IH and ID are assumed to control the green, yellow, and red indications of the signal I in the usual manner.

The decoding transformer I3 is also provided with an impulse winding i8 for energizing the impulse relay IMP when the code following'track relay CFTR is deenergizedat the end of an on period of the driven code. This impulse winding i8 is so wound and connected to the winding of the relay IMP that the momentar voltage induced therein when the relay CFTR, drops causes current to flow through relay IMP in a direction to move its contact finger l8 from the biased position, while the voltage induced in the impulse winding when the relay CF'I'R picks up merely holds the relay IMP in its biased position to the left. If it is desired to control the inversevcode independently of the occupancy of the track section, the circuit for the impulse relay IMP includes a contact l9 of the relay Y.

The operation of the relays in the transmission of a'driven and inverse'code is the same as in the conventional coded track circuit equipped for off-code transmission. Briefly stated, when the code oscillator CIBU, for example, closes its contacts for the on period, the transmitter relay CP is energized to connect the battery across the track rails and pick up the code following track relay CFTR. This reverses the energization of the primary of the decoding transformer i3 to provide energizing pulses for the relays (H and ID. When the code oscillator opens its contact and relay CP drops, the bottery 5 is disconnected before the off-code track relay OCTR is connected across the track rails; and when the code following track relay CFTR releases, the impulse relay IMP is momentarily energized in a direction to connect the battery I! to the rails to create an off-code pulse to energize the relay OCTR, this energization being only momentary so that relay OCTR assumes its deenergized biased condition before or at the time the code oscillator again closes its contacts for the next on period.

When the off code track relay OC'IR. is energized to move its contact finger 20 to the right, the primary of a transformer 2i is energized; and when the track relay releases to move its contact finger 20 to the opposite or biased position the secondary of this transformer 2| is connected through a contact finger 22 of the transmitter relay CP, closed only if said transmitter relay is deenergized, to a code responsive relay OCH of the two-position biased polar type. It is noted that when current induced in the secondary of transformer 2| when contact 20 is operated to the right cannot actuate the contacts of relay OCH because its circuit is then opened; but the current induced in the secondary of transformer 2| when contact 20 moves to the left, is of a proper direction to actuate the polar contacts of relay OCH to the right when this current flows through the relay. Briefly explaining the contemplated operation, when the track relay OCTR is operated by legitimate off-code pulses, it releases before the transmitter relay CP is energized for the next on period of the driven code, so that the impulse current in the secondary of transformer 2! acts to energize momentarily the code responsive relay OCH in a direction to momentarily actuate its contacts to the right. If, however, a stray potential of the proper polarity and intensity exists to energize effectively the track relay OC'IR,

this relay does not release when the off-code pulse ceases but remains energized until the transmitter relay CP operates to disconnect the track relay from the stray potential. Consequently, the contact finger 22 of the transmitter relay CP is in the energized position to the left at the time the impulse voltage is created in the secondary of transformer 2|, so that this impulse is not de livered to the relay OCH In this connection, the contact finger 22 of the transmitter relay CP may be arranged as illustrated to connect the secondary of transformer 2| to a discharge resistor 24, so as to avoid strains on the insulation being excessive upon circuit peak impulse voltage. The intermittent energization of the relay OCH may be relayed through a decoding transformer 39 to a slow-release repeater relay OCHP in the conventional manner as illustrated, or this relay OCH may itself be made sufficiently slow release to maintain its contact closed when energized by excessive momentary impulses from the transformer 2|.

The specific embodiment shown herein illustrates and describes the invention applied to a single coded track circuit equipped for use in various types of railway signaling systems in which it is desirable to provide a safe inverse or off code in addition to a driven code. As already indicated, the ofi-code protective check afforded by this invention is particularly useful where the off code is relied upon for safety and is cut off prior to the entrance of a train into the corresponding track section (such as provided through the control of relay Y) and it is to be understood that the present invention is intended to be applicable to such systems as may require such control as, for example, in connection with approach locking systems as specifically disclosed and described in the parent application, Ser. No. 365,065, filed November 9, 1940.

Various modifications and adaptations not illustrated or described may be made in the construc. tion and arrangement of parts and circuits illustrated without departing from the invention; and it is to be understood that the specific embodiment of the invention illustrated is merely typical and illustrative of the principle and mode of operation of the invention.

What I claim is:

1. In a coded track circuit of the character described operable at times to transmit an offcode pulse in one direction over the track rails of a track section during each oinperiod between the transmission of driven code pulses of a selected code rate in the other direction, comprising an oiT-code track relay, a transmitter relay acting when energized to connect a source of current across the track rails to provide the driven code pulses and when deenergized to connect said olf-code track relay across the track rails, code responsive means, a circuit including a back contact of said oiT-code track relay and a back contact of said transmitter relay closed only when that relay is deenergized for governing the energization of said code responsive means, and means energized through a front contact of said oiT-code track relay each time that track relay is energized and acting for a limited time following the release of such track relay for supplying energy to said circuit for said code responsive means, whereby said code responsive means receives energy through its circuit if said off-code track relay is operated and released in response to said off-code pulses, but fails to receive energy if said off-code track relay is operated and released due to stray energy in the track rails and the opera.- tion of said transmitter relay in connecting and disconnecting said off-code track relay across the track rails.

In a coded track circuit for railroads comprising, a source of current and an off-code track relay associated with one end of a track section, a transmitter relay for alternately connecting said source of current and said off-code track relay across the track rails, means for intermittently operating said transmitter relay to provide driven code pulses at a selected code rate separated by oif intervals during which the off-code track relay is connected to the track rails, means associated with the other end of said track section. and including a code following track relay responsive to the driven code pulses for at times applying a momentary off-code pulse during each off interval of the driven code and thereby energize said oif-code track relay, decoding means, and means for energizing said decoding means in response only to the intermittent operation of said ofi-code track relay and then only if that track relay releases after each energization by an off-code pulse prior to the next operation of said'transmitter relay to disconnect the off-code traclr relay from the track rails..

3.- In a coded track circuitsystem organized to transmit an inverse code pulse in one direction over the track rails of a'tracksection'during eachofi period between the transmission of succeeding driven code pulses in the other direction, a source of energy, an inverse code receiving track relay; a code transmitting relay operable at different selected code rates, circuit means controlled by said code transmitting relay for alternately connecting said track relay and said source of energy across said track rails, whereby driven code pulses are transmitted and said track relay is conditioned for receiving inverse code pulses, decoding means rendered active only upon its intermittent energization, and electric circuit a means governed by said track relay and said code transmittin relay for causing the intermittent energization of said decoding means if said track relay i energized and deenergized during the connection of said trackrelay to said track rails but acting to prevent energization of said decoding means if said track relay becomes deenergized due to its disconnection from the track rails by the operation of said code transmitting relay.

4. In a coded track circuit for railroads operable to transmit an-off-code pulse at times in one direction over the track rails of a track section during each oiT period between'the pulses of a driven code of a selected rate transmitted in the opposite direction comprising an off-code track relay adapted to be energized by the oiT-code pulses, decoding means associated with said track relay and requiring intermittent energization to be rendered active, and circuit means for energizing said decoding means with current pulses upon continued intermittent operation or said track relay by oif-code pulses, said means acting to prevent energization of said decoding means whenever said track relay fails to release within a limited time after its energization'and before the next succeeding driven code pulse, whereby said decoding means cannot be rendered active by reason of thepresence of an extraneous steady potential across the track rails.

5. In a coded track circuit for railroads, a source of current and an off-code track relay associated with the leaving end of a track section, transmitting means for alternately connecting said source of current and said track relay across the rails of said section to provide driven code pulses of a selected rate separated by off intervals and for connecting said oiT-code track relay across the rails during each oif interval for the reception of an ofi-code pulse, means including a code following track relay associated with the entering end of the track section for transmitting a momentary off-code pulse during each off interval of 'the driven code to thereby momentarily energize said off-code track relay between successive driven code pulses, code responsive means including a slow'r'elease relay maintained picked upin response to'intermittent energization, and circuit means including contacts of said track relay and said transmitting means together with auxiliary means for causing the momentary energization of said slow release relay upon each release of said track relay at the end of an off-code pulse, said circuit means preventing the momentary energization of said slow release relay if said track relay fails to release near the end of an ofi interval before the next successive driven code pulse, whereby a stray potential across said track rails causing the intermittent operation of said track relay upon its successive connections across the track rails by said-transmitting means cannot efiect the intermittent energization of said slow release relay.

6. In a coded track circuit system of the. character described wherein driven code pulses are transmitted in one direction over the track rails of a track section and an'oiT-code pulse is transmitted during each off period between successive driven code pulses, a source of current and an oil-code track relay associated with the exit end of the track section, a transmitter relay effective when actuated to one position to connect said source of current across the track rails to provide a driven code pulse and effective when actuated to the opposite position to connect said off-code track relay across the track rails of said section for the reception of an off-code pulse, code responsive means including a slow release relay requiring intermittent energization in order to be maintained picked up, circuit means, including a repeater relay, and acting through said code responsive means for momentarily energizing said slow-release relay upon each operation of such repeater relay, circuit means for said repeater relay including a back contact-of said off-code track relay and a contact of said transmitter relay closed only when that relay is in a position to connect said oiT-code track relay across the rails, and means for supplying energy to said circuit means for only a limited time following each deenergization of'said ofi-code track relay, whereby said repeater relay is operated each time said off-code track is released only providing said transmitter relay is still in said position for connecting said oil-code track relay across the rails.

'7. In a coded track circuit for railroads, a source of current and an inverse code track relay associated with one end of a track section, a transmitter relay for alternately connecting said source of current and said inverse code track relay across the track rails of the section, means for intermittently operating said transmitter relay at different selected code rates to apply driven code pulses separated by 01f intervals during which the inverse code track relay is connected to the track rails,means associated with the other end of said track section for receiving said driven code pulses and acting to apply a momentary inverse code pulse of limited duration during each ofi interval of a received driven code, whereby said inverse code track relay is intermittently operated, decoding means requiring intermittent energization inorder to be rendered active, and circuit means acting to momentarily energize said decoding means upon each release of said track relay providing such release occurs following an inverse code pulse of limited duraticn but acting to prevent such energization of said decodin g means if said track relay releases after the operation of said transmitter relay to connect said source of current across said track rails, whereby the intermittent operation of said inverse code track relay by inverse code pulses renders said decoding means active whereas the intermittent operation of said inverse code track relay due to its energization from a stray potential on the track rails during each of its connections to the track rails fails to rendcrsaid decoding means active.

3. In a coded track circuit for railroads operable to transmit an off-code pulse in one direction over the track rails of a track section during each off period between the pulses of a driven code transmitted in the opposite direction comprising, an off-code track relay adapted to be energized by the off-code pulses, energy storing means having energy stored therein While said off-code relay is energized by an oil-code pulse, a repeater relay, and circuit means for transferring the energy stored in said storing means to said repeater relay only if said off-code track relay releases during an off period.

9. In a coded track circuit for railroads operable to transmit driven code pulses of different selected rates in one direction through a track section and to transmit inverse code pulses in the opposite direction during the off periods between the driven code pulses comprising, an inverse code track relay adapted to be energized by the inverse code pulses, a repeater relay, and electric circuit means having energy stored therein While said inverse track relay is energized by an inverse code pulse and acting to transfer such energy to said repeater relay only if said track relay drops away during an off period of said driven code.

16. In a coded track relay for railroads, a source of current and an inverse code track relay associated with one end of a track section, a transmitter relay for alternately connecting said source of current and said inverse code track relay across the track rails of section, means for intermittently operating said transmitter relay at different selected code rates to apply driven code pulses separated by ofi intervals during which the inverse code track relay is connected to the track rails, means associated with the other end of said track section for receiving said driven code pulses and acting to apply a momentary inverse code pulse of limited duration during each off interval of a received driven code, whereby said inverse code track relay is intermittently operated, a repeater relay, means for storing an electric charge only when said inverse code track relay is operated, and circuit means for transferring said electric charge to said repeater relay upon the release of said inverse code track relay only if it releases before said transmitter relay operates to apply the next driven code pulse.

11. In a coded track circuit organization for railroads operable to transmit an off-code pulse in one direction over the track rails of a track section during each ofi period between the transmission of driven code pulses in the opposite direction comprising, a source of energy, an off-code track relay, a transmitter relay acting to alternately connect said source of current and said off-code track relay across the track rails to transmit a driven code pulse when in one position and to render said off-code track relay responsive to an inverse code pulse when in its opposite position, code responsive means, a circuit having its continuity controlled by said transmitter relay in said opposite position as well as by said off-code track relay in a deenergized position for governing the energization of said code responsive means, and means controlled by said off-code track relay for causing only a momentary application of energy to said circuit upon each release of said oii-code track relay, whereby said code responsive means fails to be energized unless said transmitter relay is in its said opposite position upon the release of said ofi-code track relay.

12. In a coded track circuit organization for railroads, a source of current and an inverse code track relay located at one end of a track section. a transmitter relay for alternately connecting said source of current and said inverse code track relay across the track rails of the section at different selected code rates to apply driven code pulses separated by ofi intervals during which the inverse code track relay is connected to the track rails, means associated with the other end of said track section for receiving said inverse code pulses and acting to apply a momentary inverse code pulse during each ofi interval of a received driven code, code responsive means associated with said inverse code track relay, and means eifective for only a limited time after each release of said inverse code track relay to supply energy to said code responsive means and then being efiective only if said transmitter relay is still connecting said off-code track relay across the rails of said section.

NEIL D. PRESTON. 

